Three top investors in Microsoft are taking aim at Bill Gates to step down as chairman of the company he founded nearly 40 years ago, according to reports.

The mystery backers have not been named but are understood to be lobbying the company's board of directors for Mr Gates to be replaced, unnamed sources say.

The investors are said to be of the view that Mr Gates' presence on the board is blocking the adoption of new development strategies and making it hard for the chief executive to make substantial changes.

Miscrosoft's founder handed the chief executive role to Ballmer in 2000

The news comes days after current chief executive Steve Ballmer announced he will retire within a year following pressure from backers, as the company struggles to reposition itself in the ultra-competitive tech sector.

The investors targeting Mr Gates collectively own 5% of the $277bn (£171bn) company and have stressed they are also unhappy with his role on the special committee that is searching for Ballmer's successor.

They also have misgivings that Mr Gates wields power of out of proportion to his declining shareholding, down to 4.5% now from 49% in 1986.

The company remains one of the world's most valuable tech companies

Although Microsoft is still one of the world's most valuable technology companies, its shares have remained fairly static for 10 years as Ballmer has struggled in the face of competition from Apple and Google.

This is the first time major shareholders have focused on Mr Gates, who lowered his profile at Microsoft after handing over to Mr Ballmer in 2000 to focus on his $38bn (£23bn) Bill & Melinda Gates Foundation.

One of the sources said Mr Gates was one of the technology industry's greatest pioneers, but the investors felt he had been more effective as chief executive than as chairman.